This invention relates to a current collector for a catalytic electrode and an electrochemical cell containing the electrode.
There is a variety of electrochemical cells that have catalytic electrodes. Examples include, but are not limited to, fuel cells, metal-air battery cells, gas (e.g., hydrogen) generating cells, and electrochemical sensor cells. Examples of such cells are found in U.S. Pat. Nos. 5,242,565; 5,308,711; 5,378,562; 5,567,538; 5,707,499; 6,060,196; 6,461,761; 6,602,629; 6,911,278; 7,001,689 and 7,001,865; and in International Patent Publication No. WO 00/36677.
An advantage of electrochemical cells with catalytic electrodes is that they can use one or more active materials that are not contained within cell or battery housings, thereby providing long use time (e.g., discharge capacity) with a cell having a minimum volume. For example, oxygen in the air or from another source outside the cell housing can be reduced by the catalytic electrode as part of the overall reaction of the cell. There is an ongoing desire to improve the performance of such electrochemical cells, such as by improving electrical characteristics (e.g., operating voltage, power output, energy density, discharge capacity, charging efficiency, cycle life and fade), storage characteristics, leakage resistance, cost, environmental impact of waste disposal, and safety in manufacturing.
The electrical characteristics of the electrochemical cell can be improved in a number of ways, including the use of a catalytic material having greater catalytic activity, increasing the electrical conductivity and reducing the internal resistance within the catalytic electrode. Catalytic electrodes can include an electrically conductive current collector in direct contact with the catalytic material of the electrode to reduce the internal resistance of the catalytic electrode. In the past various means have been used to minimize the internal resistance of the catalytic electrode, such as means of providing corrosion resistance of the surface of the current collector in contact with the catalytic electrode and means of providing good contact between the current collector and the catalytic portion of the electrode. For examples, the current collector surface can be coated with a metal, alloy or compound that is more corrosion resistant than the underlying substrate material, particularly when the current collector is in contact with the catalytic portion of the electrode and the cell's electrolyte. In another example, the current collector surface can be coated with particles of a conductive material such as carbon black, graphite or metal in a binder. Examples of these efforts can be found in International Patent Publication No. WO 00/36,686; U.S. Patent Publication Nos. 2006/0204839, 2005/0221190 and 2002/0132158; and in U.S. Pat. Nos. 6,403,517, 6,120,940, 4,865,925 and 4,248,682.
Previous attempts have not been completely successful in minimizing the internal resistance of catalytic electrodes and maximizing the electrical performance of cells in which those electrodes are used. Further improvement is desired, preferably in a manner that is cost effective and compatible with large scale manufacturing.